Method and device for data transfer in telecommunication system

ABSTRACT

A method and a device for transferring data in a telecommunication system comprising a data transfer path ( 8 ) and devices ( 21, 22, 1 ) using the data transfer path for data transfer, data being transferred cyclically in messages ( 4 ) between the devices according to at least one cycle having a cycle time, whereby the device ( 1 ) is configured to monitor the cyclic communication on the data transfer path; determine, on the basis of the monitoring and the cycle time of said at least one cycle of the cyclic communication, at least one expected occurrence time slot of the cyclic communication; and transmit a message not belonging to the cyclic communication to the data transfer path on the basis of at least one determined occurrence time slot such that it does not collide with one or more messages of the cyclic communication occurring in the determined at least one occurrence time slot.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of PCT/FI02/01024, filed Dec. 14,2001.

BACKGROUND OF THE INVENTION

The invention relates to a method and a device for data transfer in atelecommunication system, and particularly to data transfer in atelecommunication system wherein data is transferred cyclically.

An example of a telecommunication system wherein data transfer takesplace cyclically in accordance with certain cycle times is aconventional factory automation system comprising a programmable logiccontroller (PLC or a so-called SoftPLC, which means replacing aprogrammable logic execution unit by an application program to be run ina computer for the execution of the commands issued by a logic program),related actuators and sensors or other devices, as well as a bus, e.g. abus called Profibus or the like, connecting these. Typically, theinternal telecommunication of such a system is cyclic such that thetransmitter of data, e.g. a PLC, transmits a certain (the same) messageat certain intervals in accordance with a corresponding cycle time, i.e.in other words a cycle time refers to the time between the startingmoments of transmission of two such successive messages. A message isdelivered to a device connected to the bus, and the device typicallyreplies by transmitting a reply message. When the cycle time is shortenough, data can thus be transferred practically in real time e.g.between a PLC and another actuator, in which case e.g. the real timestatus information or the like on the actuator is available to the PLC.There are usually several such cycles in progress simultaneously, eachhaving a certain cycle time. The cycle times of different cycles maydiffer from each other or they may be equal in length. In addition, insuch a system a message cycle is usually always started by a deviceoperating as a master, such as a PLC, while the rest of the devices onlyreply to the messages supplied from the master device. In such a case,each message cycle has a predetermined transfer time on a data transferpath, thus enabling collisions between messages, i.e. simultaneoustransmissions to a data transfer path, to be prevented.

Development of data transfer systems and the Internet, for example, haveenabled e.g. different remote control systems to be implemented in asimpler manner such that an automation system connected to ageneral-purpose telecommunication network, such as an Ethernet network,can be monitored and controlled from a control system also connected tothe particular network. Furthermore, if the Ethernet network or the likeis connected to the Internet, the control system can be connected to thesystem to be controlled via the Internet.

A problem with the above-described system is how to connect atelecommunication system based on cyclic data transfer to ageneral-purpose telecommunication system wherein message communicationis not based on any regular cycles but takes place as necessary and e.g.in dependence on the load situation in the network. If a message comingoutside the system, e.g. via the Internet, is to be delivered to thetelecommunication system based on the described cyclic data transfer,and such a message is transferred directly to the system, it is possiblethat the message may collide with a message of the cyclic communicationsince no time slot is reserved in the system based on cyclic datatransfer for such a message coming from outside. Furthermore, the largerthe number of such messages of random character coming from outside adeterministic telecommunication system based on cyclic data transfer andbeing delivered to the system, the larger the average number ofcollisions between messages coming from outside and internal cyclicmessages of the telecommunication system, in which case the internaldata transfer of the telecommunication system becomes increasinglydisturbed.

A prior art solution to this problem is disclosed in publishedapplication WO 99/13388 which discloses a device for controlling thecommunication between two telecommunication networks. In the solutiondisclosed in the publication, a particular intermediation device (proxydevice) controls messages supplied to a deterministic network within acertain quota such that it only lets in a certain number of messagesduring a certain time period. The transfer quota of a device ispredetermined according to the load situation of the network.

The problem potentially relating to this prior art solution is, however,that the solution is based on the assumption that by distributing thecommunication coming from outside a deterministic network evenly withina certain quota, the disturbances caused by the communication comingfrom outside to the internal communication of the network can beminimized within a certain probability. Particularly when the load ofthe network is high, collisions may nevertheless occur disturbinglyoften since the transmission path of the network is highly loaded,meaning that not much free transfer time exists, and the messagesdiffering from the cyclic communication and coming from outside to thetransmission path do not necessarily meet the free time slots of thecyclic communication often enough.

BRIEF DESCRIPTION OF THE INVENTION

An object of the invention is thus to provide a method and an apparatusimplementing the method so as to solve the above-mentioned problems orso as to at least alleviate the problems. The object of the invention isachieved by a method and a device which are characterized by what hasbeen disclosed in the independent claims 1 and 8. Preferred embodimentsof the invention are disclosed in the dependent claims.

The invention is based on monitoring cyclic communication on atransmission path of a telecommunication system and determining, on thebasis of this and a cycle time or cycle times of the cycliccommunication that in a normal state remain substantially constant, atleast one or more expected occurrence time slots of the cycliccommunication. A message not belonging to the cyclic communication, e.g.a message coming from outside the telecommunication system, can then, onthe basis of the determined expected occurrence time slots of the cycliccommunication, be transmitted to the data transfer path such that themessage does not collide with one or more messages of the cycliccommunication occurring in the determined occurrence time slots. Duringthe normal state of the system, wherein the cycle times aresubstantially constant, the occurrence time slots of the cycliccommunication can be determined in a highly reliable manner and thusinterleave the rest of the communication with the cyclic communication.

An advantage of the method and system of the invention is that theinvention enables communication not belonging to cyclic communication tobe transferred on a transmission path used by cyclic communication suchthat the cyclic communication is disturbed as little as possible.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described in closer detail in connection with thepreferred embodiments and with reference to the accompanying drawings,in which

FIG. 1 is a block diagram showing a telecommunication system whereto theinvention can be applied;

FIG. 2 is a block diagram showing a second telecommunication systemwhereto the invention can be applied;

FIG. 3 is a diagram showing an occurrence time slot of a message inaccordance with an embodiment of the invention; and

FIG. 4 is a diagram showing transfer of an occurrence time slot of amessage in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a telecommunication system comprising a telecommunicationnetwork 2, which is e.g. an automation system and which furthercomprises a master unit 21 and a number of slave units 22 connected toeach other by means of a data transfer path 8. The data transfer path 8may be a wired transmission path, e.g. a bus used in automation systems,or a wireless transmission path, such as a radio path. The master unit21 is e.g. a programmable logic controller PLC and the slave units 22are e.g. actuators and sensors or other devices connected thereto. Theinternal data transfer of the network 2, i.e. the data transfer betweenunits 21 and 22, operates cyclically, in which case a message cycle 4 isalways initiated by the master unit 21 while the rest of the units 22only reply to the messages supplied from the master unit 21, asillustrated in the figures and as described already in the general partof the description. The internal data transfer of the network 2 thustakes place completely controlled by the master unit 21. Each messagecycle 4 thus has a predetermined transfer time on the data transfer path8 and thus collisions between different messages, i.e. simultaneoustransmissions to the data transfer path, can be prevented. The network 2is further connected to an intermediation device 1, which may be e.g. arouter or a switch or another network device. Through the intermediationdevice 1 the network 2 is connected to other systems 3, such as othertelecommunication networks, such as the Internet. The functionality ofthe invention is implemented at the intermediation device 1 and it ispreferably implemented by software by means of a processor and suitablesoftware or, alternatively, by separate components or circuits. If thedevice 1 is e.g. a router or a switch or a corresponding network device,the functionality of the invention may be added thereto e.g. in the formof a suitable software update. It is to be noted that the figures onlyshow elements relevant to the understanding of the invention; theapplication of the invention is by no means restricted to the systemsdisclosed herein.

According to the basic idea of the invention, the intermediation device1 monitors the internal communication 4 of the network 2 on the datatransfer path 8. The intermediation device 1 also preferably analysesthe communication and stores the analysis results obtained in itsmemory. Furthermore, the intermediation device 1 preferably monitors therealization of the obtained analysis results and corrects them if thecommunication changes, i.e. preferably, the communication is analysedcontinuously. Communication 6 coming from outside the network 2 is firstbuffered to the intermediation device 1. After noticing, on the basis ofthe analysis information, that a sufficient pause exists in the internalcommunication of the network 2, the intermediation device 1 transmitsthe message it has buffered to the data transfer path 8 of the network2. Outgoing communication 5 from the network 2 can be forwardedimmediately.

The internal communication of the network 2 is thus cyclic. It istransmitted e.g. by a process at the master unit 21. Normally, theprocess delivers the data to be transmitted to a protocol stack.Usually, a protocol stack also operates cyclically. Since theintermediation device 1 connected to the transmission path 8 hears allmessages from the transmission path, it is possible to analysemathematically e.g. the cycle times and occurrence moments of cyclicdata on the transmission path.

A cycle time or cycle times of the internal communication of the network2 can be supplied to the intermediation device 1 or, alternatively, theintermediation device may determine a cycle time or cycle times itself.If the cycle times are supplied to the intermediation device 1, it ispreferably also provided e.g. with the cycle time of a protocol stack,if one exists. When the cycle times are supplied to the intermediationdevice 1, it does thus not have to carry out mathematical calculation inorder to find out a cycle time or cycle times. The only matter subjectedto mathematical analysis is then the anticipation of an occurrence timeslot or occurrence time slots of the cyclic communication 4 in the bus8.

When the intermediation device 1 is to determine the cycle times of theinternal communication 4 itself, the cycle time of the operation of apossible protocol stack may also then be supplied to the intermediationdevice 1 (or information indicating that the protocol stack has no cycletime but the process using data transfer starts the protocol stackitself) or the intermediation device may also determine its cycle timeitself.

When the intermediation device, by means of historical events, is todetermine the cycle time of the data transfer of the internalcommunication itself, the following assumptions are preferably used:

A cycle time is usually no indefinite number, e.g. 29.38 ms, buttypically an even round figure, such as 50 ms.

In a normal process situation, the cycle time does not change butremains substantially constant.

In a normal process situation, the system tries to settle in a stablestate, i.e. changes occurring in the system are not continuous but suchchanges occur periodically. Such changes may occur e.g. when twodifferent processes, the cycle time of the slower one of the processesbeing a multiple of the faster one, communicate to the outside world, inwhich case the mutual order between the messages transmitted by theseprocesses in the bus 8 may change occasionally while the messages of theprocess having a slower cycle time may also be delayed from theanticipated cycle time. These phenomena do not, however, have any effecton the actual cycle time but on the occurrence moment of data in the bus8.

A cycle time or cycle times are preferably determined such that theintermediation device 1 monitors the communication in the bus 8 andmonitors each message cycle, simultaneously sampling the times betweensuccessive messages of each message cycle, i.e. more specifically, thetimes between the starting moments of successive messages. When asufficient number of samples has been taken from a certain cycle, themean value of the samples approaches the real cycle time of theparticular cycle. Taking also the above-disclosed assumptions intoaccount, the cycle time of the cycle can thus be found out. If severalcycles are in progress, the cycle time of each cycle is preferablydetermined.

In calculating the cycle time of a protocol stack, if the intermediationdevice is to determine it, a message having the most frequent cycle ispreferably used. Its standard deviation should be close to the cycletime of the protocol stack divided by two. The same usually applies tothis time as to the cycle time of processes, i.e. it is a round number.It can also be inferred from the value obtained whether or not aprotocol stack resides in its own process. If the value is small, theprotocol stack does not reside in its own process. When the value is areal one, it is preferably rounded to the closest round number, e.g. 50μs. If the value is not even close to any round number, more samples aretaken and the calculation is repeated. The value obtained can be usedfor checking the calculations.

In the bus 8 of the cyclic communication 4, the predetermination of acoming occurrence time slot or slots can be based on the assumption thatthe occurrence moment of a message of a certain cycle from the previousoccurrence follows a normal distribution. An alternative is to use thecycle time of a protocol stack, if one exists, as the range ofvariation. A variable x should, however, be added to this cycle time,the value of the variable x increasing as the number of faster cycletimes increases.

Another alternative is to use normal estimators of a normaldistribution:

$\begin{matrix}{{Z = {\frac{\overset{\_}{X} - \mu}{\sigma/\sqrt{n}} \sim {N\left( {0,1} \right)}}},} & (1)\end{matrix}$

wherein σ=√{square root over (s²)}, i.e. the square root of a samplevariance,

X is the sample mean value, and

n is the sample size used.

The sample variance is obtained from the formula:

$\begin{matrix}{s^{2} = {{\frac{1}{n - 1}\left\lbrack {{\sum\limits_{i = 1}^{n}x_{i}^{2}} - {\frac{i}{n}\left( {\sum\limits_{i = 1}^{n}x_{i}} \right)^{2}}} \right\rbrack}.}} & (2)\end{matrix}$

X, in turn, is obtained from the formula:X =(x ₁ +x ₂ +x ₃ + . . . +x _(n))/n.  (3)

When the intermediation device 1 is given a probability P to use, a timeslot can be calculated wherein the message of the cyclic communicationshould occur. After this time slot has started, i.e. after it has becomeactive, preferably no outside messages 6 are allowed to enter the bus 8.After the message of the cyclic communication has passed, other messagesmay preferably be allowed to enter the bus. Therefore, the predeterminedtime slot of the message of the cyclic communication is preferablycancelled, i.e. it becomes non-active, when the related message haspassed in the bus, even though the time reserved for the time slot hadnot exhausted completely. The message of the outside communication canthus be allowed to enter the bus as soon as the time slot of the messageof the cyclic communication is cancelled; or all the current active timeslots are cancelled if the number of active time slots is larger thanone. The prerequisite is thus that no time slot of the cycliccommunication is active, i.e. transmission of the message not belongingto the cyclic communication to the bus 8 is preferably not startedbefore the all the current active time slots of the cyclic communicationare cancelled. In addition, the message not belonging to the cycliccommunication is transmitted to the data transfer path 8 such that thetransfer of the message on the data transfer path ends before the startof a next determined coming occurrence time slot of the cycliccommunication. In some bus types, such timing of the transfer of amessage before the start of the transfer of a next message may be aproperty of the bus 8 itself, which means that the intermediation device1 may ignore it. The probability P is preferably selected such that whenthe volume of communication is small, a greater probability P can beused since free time for outside communication exists in any case. Agreater probability P reduces the risk of collisions. When, on the otherhand, the volume of communication is large, a smaller probability P mustbe used since not so many time slots are left to be used by outsidecommunication. This increases the risk of collisions, though.Preferably, a suitable default value is used for the probability P,which can be changed, if necessary. An occurrence time slot μ can becalculated e.g. in the following manner:X−Z _(?) σ/√{square root over (n)}−K≦μ≦ X+Z _(?) σ/√{square root over(n)}+timeout−K,  (4)

wherein Z_(?) is the tabular value of a normal distribution of a givenprobability and ? is obtained from the formula:?=1−(1−P)/2.  (5)

In equation 4, the value timeout should be at least equal to theexecution time of processes having higher priorities, multiplied by thenumber of executions that can be contained between the cycle of theprocess being processed. In FIG. 3, a time line is used for illustratingan occurrence time slot μ such that the left side of equation 4 isdesignated by the letter A while the right side without parameterstimeout and K is designated by the letter B, the middle point thereofthus being X. In addition, a timeout period is designated on the timeline. The parameter K contained in equation 4 is a correction parameterwhich enables the realized occurrence moments to be taken into accountand the deviations therein to be corrected compared with previousanalysis results. K is the interval of a previous execution subtractedby a function of the time slot without timeout. In other words, if theexecution slot does not meet the time slot A+B, the difference issubtracted preferably from the next expected occurrence time since themean value of the execution intervals is usually within the range of acouple of decimals from the programmed one when the sample size is tenor more. When the occurrence moment of a message meets the time slotA+B, the value of K is, correspondingly, zero. This is illustrated inFIG. 4 which shows the occurrence of time slot n and the following timeslot n+1 on two time lines. The time lines are aligned on top of eachother such that the lower time line corresponds to the upper one addedby the cycle time of the message under examination. The realizedoccurrence moment of the message is designated on the upper time line,which occurrence moment takes place in a timeout sequence. The value ofK is the time between time slot A+B and the real occurrence moment ofthe message, as shown in the figure, and the next time slot n+1correspondingly moves earlier by the magnitude of K.

Only one possible example has been disclosed above for determining acoming occurrence time slot or slots, but it is obvious that other kindsof methods can also be used without deviating from the basic idea of theinvention.

FIG. 2 shows a second telecommunication system to which the inventioncan be applied. The system of FIG. 2 is otherwise similar to that ofFIG. 1 but several networks 2 are connected to the intermediation device1, the internal structure of each of the networks corresponding e.g.with the network 2 shown in closer detail in FIG. 1. In the following,these separate parallel networks 2 will be called sectors.

In the system of FIG. 2, the following properties may preferably beadded to the intermediation device 1: transfer and mastering of thetiming of a controlled sector 2. The transfer of timing of controlledsectors 2 enables communication 7 between the sectors 2 to be matched insuch a way it does not disturb the internal communication of thecontrolled sectors 2. The mastering of the controlled sector 2 enablescomplexity of internal communication structure (multimaster) to beprovided for the internal communication structure of the sector 2.Without mastering, in the system of FIG. 2 the intermediation device canbe used for controlling master-slave communication, as described abovein connection with FIG. 1. In such a case, the communication 7 betweenthe controlled sectors 2 is processed in the intermediation device 1, asthe communication 6 coming from elsewhere outside 3.

In the multimaster mode, also the communication 7 between the sectorscan be processed as internal communication and only the communication 6coming from outside the sectors is processed as outside communication,which is buffered to the intermediation device, as described above. Themultimaster mode of the intermediation device can be implemented in theintermediation device 1 e.g. in the following manner: First, theintermediation device 1 device finds out the master units 21 from eachsector 2 and the communication 4 thereof. Based on this, analysis datarecords are created on the communications. The analysis data records areupdated on the basis of information on real, listened-to communication.In the multimaster mode, the intermediation device 1 gives the masterunit 21 of each sector 2 its own communication time blocks to befollowed by the devices. The intermediation device 1 may then, bymonitoring the communications, ensure that the communication time blocksremain in place. If the monitoring result starts to slide too much, theintermediation device 1 gives a zero pulse and the master units 21return to the original time blocks. Another alternative is that a timeror a network device gives each master unit 21 in turn a chance to carryout its own communications.

Information security properties, for example, may also be added to theintermediation device 1 since it is invisible to the transmission path.The invisibility of the intermediation device enables variouscommunication filters to be built without enabling the properties of thefilters to be modified by means of the communication to be deliveredtherethrough.

The invention may also be applied to different telecommunication systemsbased on a radio path. Bluetooth systems and WLAN (Wireless Local AreaNetwork) systems based on IEEE 802.11 recommendation, for example, usepartly the same 2.45 GHz frequency range. A Bluetooth system istypically intended for short, less than 10 m connections betweendevices. A WLAN system, on the other hand, is intended for providing awireless local area network connection, and the connection distances thesystem enables may usually be dozens or hundreds of metres. Thesesystems are often used in the same areas of use, either as separatesystems or as a combination thereof. An example of a combination of thesystems is an arrangement wherein a terminal device, via a Bluetoothlink, communicates with a WLAN intermediation residing in the vicinity,e.g. in the same room, the WLAN intermediation, in turn, having a WLANconnection to a service provider residing farther away and providinge.g. an Internet connection. Since the Bluetooth and WLAN systems use aradio path partially having the same frequency, it may happen that theyinterfere with each other's communications. In such a case, theinvention may be utilized e.g. in connection with the WLANintermediation such that the WLAN intermediation analyses the cycliccommunication of the Bluetooth system occurring on the radio path andmatches its transmission of WLAN messages to the radio path in betweenthe Bluetooth communication such that the Bluetooth and WLANcommunications do not collide on the radio path.

It is obvious to one skilled in the art that as technology advances, thebasic idea of the invention can be implemented in many different ways.The invention and its embodiments are thus not restricted to theabove-described examples but may vary within the scope of the claims.

1. A method of transferring data in a telecommunication systemcomprising a data transfer path and devices using the data transfer pathfor data transfer, data being transferred on the data transfer pathcyclically in messages between the devices according to at least onecycle having a cycle time remaining substantially constant, wherein thecycle time of a cycle is a time between starting moments oftransmissions, by the same transmitter, of two successive messagesbelonging to the cycle, the method comprising: monitoring the cycliccommunication on the data transfer path of the telecommunication system;determining, on the basis of the monitoring and the cycle time of saidat least one cycle of the cyclic communication, at least one expectedoccurrence time slot of the cyclic communication, wherein saiddetermining comprises: detecting, on the basis of the monitoring, one ormore messages belonging to a particular cycle of the cycliccommunication; determining a realized occurrence moment of the detectedone or more messages; and determining, on the basis of the realizedoccurrence moment of the detected one or more messages and the cycletime of that particular cycle, an occurrence time slot, which isexpected at a predetermined probability, of at least one next messagebelonging to that particular cycle; and transmitting a message notbelonging to the cyclic communication to the data transfer path on thebasis of at least one determined occurrence time slot of the cycliccommunication such that it does not collide with one or more messages ofthe cyclic communication occurring in the determined at least oneoccurrence time slot.
 2. The method of claim 1, wherein the message notbelonging to the cyclic communication is transmitted to the datatransfer path such that the transfer of the message on the data transferpath ends before the start of the next determined coming occurrence timeslot of the cyclic communication.
 3. The method of claim 1 or 2, whereinthe occurrence time slot determined for the next message of the cycliccommunication is changed into non-active after the next message haspassed on the data transfer path, the message not belonging to thecyclic communication being transmitted to the data transfer path suchthat the transmission of the message not belonging to the cycliccommunication does not start before the current occurrence time slot ofthe cyclic communication becomes non-active.
 4. The method of claim 1 or2, wherein the occurrence time slots of the cyclic communication aredetermined for each cycle.
 5. The method of claim 1 or 2, wherein themethod further comprises: determining, on the basis of the monitoring,the cycle time of said at least one cycle of the cyclic communication onthe data transfer path of the telecommunication system prior todetermining the occurrence time slots of the cyclic communication. 6.The method of claim 5, wherein the cycle time of the cycle is determinedon the basis of the times between occurrence time slots of two or moredetected messages belonging to the cycle.
 7. A device for transferringdata in a telecommunication system comprising a data transfer path anddevices using the data transfer path for data transfer, data beingtransferred on the data transfer path cyclically in messages between thedevices according to at least one cycle having a cycle time remainingsubstantially constant, wherein the cycle time of a cycle is a timebetween starting moments of transmissions, by the same transmitter, oftwo successive messages belonging to the cycle, the device comprising:means for monitoring the cyclic communication on the data transfer pathof the telecommunication system; means for determining, on the basis ofthe monitoring and the cycle time of said at least one cycle of thecyclic communication, at least one expected occurrence time slot of thecyclic communication, said means for determining comprising: means fordetecting, on the basis of the monitoring, one or more messagesbelonging to a particular cycle of the cyclic communication; means fordetermining a realized occurrence moment of the detected one or moremessages; and means for determining, on the basis of the realizedoccurrence moment of detected one or more messages and the cycle time ofthat particular cycle, an occurrence time slot, which is expected at apredetermined probability, of at least one next message belonging tothat particular cycle; and means for transmitting a message notbelonging to the cyclic communication to the data transfer path on thebasis of at least one determined occurrence time slot of the cycliccommunication such that it does not collide with one or more messages ofthe cyclic communication occurring in the determined at least oneoccurrence time slot.
 8. The device of claim 7, wherein the means fortransmitting are configured to transmit the message not belonging to thecyclic communication to the data transfer path such that the transfer ofthe message on the data transfer path ends before the start of the nextdetermined coming occurrence time slot of the cyclic communication. 9.The device of claim 7 or 8, wherein the occurrence time slot determinedfor the next message of the cyclic communication changes into non-activeafter the next message has passed on the data transfer path, and whereinthe means for transmitting are configured to transmit the message notbelonging to the cyclic communication to the data transfer path suchthat the transmission of the message not belonging to the cycliccommunication does not start before the current occurrence time slot ofthe cyclic communication changes into non-active.
 10. The device ofclaim 7 or 8, wherein the means for determining at least one expectedoccurrence time slot of the cyclic communication are further configuredto determine the occurrence time slots of the cyclic communication foreach cycle.
 11. The device of claim 7 or 8, wherein the means fordetermining at least one expected occurrence time slot of the cycliccommunication are further configured to determine, on the basis of themonitoring, the cycle time of said at least one cycle of the cycliccommunication on the data transfer path of the telecommunication systemprior to determining the occurrence time slots of the cycliccommunication.
 12. The device of claim 11, wherein the means fordetermining at least one expected occurrence time slot of the cycliccommunication are further configured to determine the cycle time of thecycle on the basis of the times between occurrence time slots of two ormore detected messages belonging to the cycle.
 13. The device of claim 7or 8, wherein the device is a router.
 14. The device of claim 7 or 8,wherein the device is a switch.
 15. The device of claim 7 or 8, whereinthe data transfer path is a radio path and the device is a transceiver.